The present invention relates generally to oil seals and more particularly, to so called heavy-duty rotary end face seals designed for application in severe service environments wherein conditions of soil, weather, etc., are destructive of seals and sealed mechanisms. The invention comprises an improvement over known heavy-duty grit seals of a similar nature, such as seals of the type shown in U.S. Pat. No. 3,241,843, and other patents.
Seals of the type with which the invention is concerned are commonly used to exclude water, sand, grit and the like from lubricated assemblies used on earthmoving equipment. Typically, the seals are used in track rollers and final drives of track laying vehicles such as bulldozers, shovels, drag ling buckets, etc. The rollers, idlers, and final drives of such vehicles are commonly exposed to mud, dust, sand and rocks, and are often called upon to operate or stand under water, and to operate in other conditions which vary from desert to the arctic environments. Such seals are successful because even under these conditions, they are able to exclude the grit and other material in the working environment from the sealed parts, namely, the bushings, rollers, or the like.
Unquestionably, the most successful types of seals used in these applications have been those which use one or two ring-like rubber members to support oppositely directed, cooperating metal primary seal rings. Typically, a seal of this type includes a pair of annular rings having frustoconical cross sections and made from a synthetic elastomer, with a pair of annular abrasion resistant metal rings of L-shaped cross section being supported by the rubber members and having the radially extending, axially facing end portion of the metal rings in abutting end face relationship.
According to this seal concept, the outer diameters of the rubber rings, which act as a secondary seals, are received in place within counter-bores on adjacent, relatively movable parts of the vehicle. When the installation is complete, the sealed parts are moved axially together so that the seal assembly as a whole undergoes axial compression, and because of the configuration of the rubber members, a radial compressive load is applied to the axially extending flanges of the primary seal rings by the inner diameters of the rubber rings.
In use, as a certain amount of axial movement takes place, the rubber rings are compressed to a greater or less extent between two extremes. The geometry, size and composition of the rubber members are arranged such that, with the seal being most tightly compressed, the axial load applied to the opposed metal working faces of the seal will not be so high so as to create undue resistance to rotation and consequent overheating, while under conditions of the least anticipated axial compression, a predetermined minimum axial force is provided to prevent outward leakage of oil and ingress of grit particles and/or water between the seal faces. The difference between the maximum and minimum axial thickness of the seal assembly is a distance referred to as the working range or working height range of the seal.
Because of the structural characteristics of the rubber rings, the working range of this type of seal is generally quite large. The rubber and metal parts both provide excellent abrasion resistance, and consequently, seals of this type commonly last for the entire working life of the sealed part.
As is the case with almost every engineered product, however, there have been certain conditions which occasionally have created premature wear and/or potential failure in seals of the type just described.
One such problem in particular has been that, as the external seal cavity continually works in a severe environment, it fills completely with grit, sand, water, mud, etc. The area radially outside of the seal becomes tightly packed with such material, or such material enters in the fluid state and becomes frozen in place. When excessive mud is packed between radial flanges of the metal rings and exposed exterior faces of the rubber rings, the effective spring rate or stiffness of the rubber parts in axial compression increases to such an extent that the seals may be compressed beyond their design limit, thereby wearing out prematurely in use. In addition to this mode of failure, the mud pack may dislodge the rubber rings from the metal rings and cause leakage.
Consequently, in view of the foregoing shortcomings of certain forms of prior art seals, it is an object of the invention to provide an improved heavy duty grit seal.
Another object is to provide a heavy duty seal unit which will minimize cost and expense in use.
A still further object of the invention is to provide a seal in which the secondary members include especially adapted portions intended to cover those parts of the sealing mechanism which are required to be maintained in a flexible condition.
A still further object is to provide a seal in which the elastomeric and metal parts have cooperating surfaces which serve to define between them a recess or grit-free area which will allow movement from time to time of parts of the sealed member which, in effect, act as springs for the primary seal members.
A still further object is to provide a seal unit wherein the rubber members include a lip or flange adapted to be received over the radially outer end of a generally radially extending flange of the primary seal ring with the lip or flange having an end portion which is adapted to move axially as the rubber seal portion expands and compresses axially.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a seal unit having a primary seal ring with a generally L-shaped configuration and an annular secondary seal ring of generally parallelogram cross section, with the secondary seal ring further including an integrally formed lip or flange adapted to extend over the radially outer part of the primary seal ring so as to prevent foreign material from lodging between an outer face of the secondary seal and one radial face of the primary seal ring.
The manner in which these and other objects and advantages are achieved in practice will be more clearly understood when reference is made to the following detailed description of the preferred embodiment of the invention set forth by way of example and shown in the accompanying drawings in which like reference numbers indicate corresponding parts throughout.